The floating zone (FZ) technique changed from a crucible-free purification method into a growth technique mainly for high purity silicon crystals. The melt zone is inductively heated by the high frequency magnetic field of a sophisticated one-turn induction coil being the heart of the FZ growth. The needle-eye technique allows for crystals with large diameters beyond the capillary limitations of a cylindrical zone, but both electric breakthrough at the coil slit and bursting of the crystal by thermomechanical stress presently limit the diameter to 200 mm. A novel gFZ concept is depicted that works with granular silicon feedstock instead of expensive feed rods. The automation of the industrial FZ silicon growth is a key issue regarding yield, reproducibility, quality, and economization. A model-based, predictive control system of the FZ growth is presented. For state-of-the-art development and to overcome the process barriers, a detailed multiphysical numerical modeling of the FZ process is required and outlined.

Commonly, germanium crystals are grown after the Czochralski (CZ) method. The crucible-free pedestal and floating zone (FZ) methods, which are widely used for silicon growth, are hardly known to be investigated for germanium. The germanium melt is more than twice as dense as liquid silicon, which could destabilize a floating zone. Additionally, the lower melting point and the related lower radiative heat loss is shown to reduce the stability especially of the FZ process with the consequence of a screw-like crystal growth. We found that the lower heat radiation of Ge can be compensated by the increased convective cooling of a helium atmosphere instead of the argon ambient. Under these conditions, the screw-like growth could be avoided. Unfortunately, the helium cooling deteriorates the melting behavior of the feed rod. Spikes appear along the open melt front, which touch on the induction coil. In order to improve the melting behavior, we used a lamp as a second energy source as well as a mixture of Ar and He. With this, we found a final solution for growing stable crystals from germanium by using both gases in different parts of the furnace. The experimental work is accompanied by the simulation of the stationary temperature field. The commercially available software FEMAG-FZ is used for axisymmetric calculations. Another tool for process development is the lateral photo-voltage scanning (LPS), which can determine the shape of the solid–liquid phase boundary by analyzing the growth striations in a lateral cut of a grown crystal. In addition to improvements of the process, these measurements can be compared with the calculated results and, hence, conduce to validate the calculation.

In numerical simulations of the floating-zone crystal growth process, the shape of phase boundaries is unknown beforehand and must be obtained as a part of the solution. One of the factors, which may influence the shape of phase boundaries significantly, is convective heat transfer in the molten zone. The present paper offers an analysis based on mathematical modelling of the influence of the melt motion on the shape of phase boundaries by investigating a specific 2" floating zone growth system and compares the modelling results with experiment. A needle-eye inductor is used in the growth system leading to curved boundaries of the molten zone and to strong high-frequency electromagnetic forces in the melt. The influence of the melt motion on the crystallization interface is also estimated analytically.

During the unification of the two German states, in January 1992, the Institute of Crystal Growth (IKZ) in Berlin was founded. The activities of about one hundred co-workers focus on bulk and epitaxial growth of crystalline materials, beginning from the basic research up to the technological realization. At present the research topics are: silicon, SiGe, SiC, GaAs, ZnSe, GaPO4, oxide crystals, numerical simulation, preparation, characterization and development of growth equipment. As such IKZ could be seen as a one of a kind institute in the world.